1. Field of the Invention
Exemplary aspects of the present disclosure relate to a serial communication apparatus, and more particularly to an apparatus for RS-232C and RS-485 serial communication using common communication port configured to selectively use a communication by two methods without change in external wirings by performing the RS-232C and RS-485 communications using a common communication port.
2. Description of Related Art
A serial communication is widely used in various fields including a PLC (Programmable Logic Controller), and the serial communication is generally implemented using RS-232C or RS-485 serial communication method.
FIG. 1 is a block diagram illustrating an example of a serial communication apparatus disposed with one RS-232C channel and one RS-485 channel, where communication with an external communication apparatus is implemented using an embedded UART (Universal Asynchronous Receiver/Transmitter) of an MPU (Micro Processor Unit, 11), an RS-232C driver (12) and an RS-485 driver (13), and an RS-485+ signal and an RS-485− signal are created and transmitted to output ports when a transmission control signal is high, and received data is transmitted to an MPU (Micro Processor Unit, 11) via an input port when the transmission control signal is low.
That is, a signal in channel 1 is converted to a RS-232C level via the RS-232C driver (12) to perform an RS-232C communication, and a signal in channel 2 is converted to an RS-485 level via the RS-485 driver (13) to perform an RS-485 communication. At this time, the channel 1 can implement the communication using only the RS-232C method, and the channel 2 can implement the communication using only the RS-485 method, because a signal level of the RS-232C method and a signal level of RS-485 method are different.
As noted from the foregoing, because each terminal of communication ports is functionally fixed according to a communication method, RS-232C communication channel and RS-485 communication channel are fixed in the hardware manner, whereby several types of communication modules are required depending on used communication methods.
Furthermore, the prior art suffers from various disadvantages and problems in that types of communication modules must be changed in order to change a channel using an RS-232C method to a channel using an RS-485 method, or to change a channel using an RS-485 method to a channel using an RS-232C method, and wirings of each terminal must be replaced, to name a few.